The building trade and related industries consume many square feet annually of wood and metal materials which require protective coatings. One of the most used wood materials is hardboard which is made from ground or chipped wood fibers mixed with a suitable cohesive and pressed. The hardboard surface is coated to improve weather resistance, water and solvent resistance and hardness. Typically, the coating systems are solvent-based resin compositions. The use of such compositions required extra safety and health precautions to reduce solvent escape into the air. A water-based coating composition would be less toxic and less polluting.
In an attempt to prepare a good water-based (i.e. latex) coating composition, reactive acrylic ester latexes were mixed with thermoset resins. Unfortunately, the use of a urea-formaldehyde type thermoset resin did not yield coating compositions that provided adequate water resistance after cure. The use of melamine-formaldehyde thermoset resins in the latices yielded coating compositions that provided improved water-resistant coatings, but the latex composition was not stable, often gelling within one day. It was unexpectedly found that the use of a combination of a urea-formaldehyde and a melamine-formaldehyde thermoset resin in a reactive acrylic ester polymer latex yields stable latex coating compositions that provide, upon cure, improved water and chemical resistant coatings.